An example of a conventional speaker device that enhances low-pitched sound include one having a phase inversion type enclosure provided with a bass reflex port (see Patent Document 1, for example).
However, as the size of a speaker device and cross-sectional area of a bass reflex port are reduced, the flow velocity of air inside the port is increased accordingly, and noise resulting from airflow is more likely to occur, so that vortex ring airflow bursts out of an opening of the port. Further, when the flow velocity of air inside the port is increased, airflow resistance inside the port is also increased, and low-pitched sound enhancement effect is reduced. Therefore, in a small-size speaker device, a bass reflex port is rarely used.
On the other hand, Patent Document 2 proposes a speaker device in which the flow velocity of air inside a port is reduced by devising the shape of the port, thus allowing a bass reflex port to be used even in a small-size speaker device.